The objective of the study is to assess the efficacy of eight NO-releasing NSAIDs to reduce or inhibit colon carcinogenesis as measured by the aberrant crypt foci assay using male Fisher 344 rats treated in accordance with the two protocols described below. Measure aberrant crypt formation before and after the first carcinogen exposure, according to methods of Tudek, Bird, and Bruce. Eight week old rats are injected twice with15 mg of azoxymethane (AOM) per kg of body weight one week apart. The chemopreventive agent is administered beginning at 4 weeks after the first carcinogen dose and for another four weeks. the number of aberrant crypt foci per small intestine and for colon are determined. Also the number of aberrant crypts per foci from unsectioned methylene-blue stained tissue under low power light microscopy are being determined. The relative colon cancer chemoprevention efficacy using the three agents are being determined which were most effective in the crypt assay.